Orthogonally Functionalizable Polyurethane with Subsequent Modification with Heparin and Endothelium-Inducing Peptide Aiming for Vascular Reconstruction

Facile engineering of interactive double network hydrogels for heart valve regeneration

Regenerative heart valve prostheses are essential for treating valvular heart disease, which requested interactive materials that can adapt to the tissue remodeling process. Such materials typically involves intricate designs with multiple active components, limiting their translational potential. This study introduces a facile method to engineer interactive materials for heart valve regeneration using 1,1'-thiocarbonyldiimidazole (TCDI) chemistry. TCDI crosslinking forms cleavable thiourea and thiocarbamate linkages which could gradually release H2S during degradation, therefore regulates the immune microenvironment and accelerates tissue remodeling. By employing this approach, a double network hydrogel was formed on decellularized heart valves (DHVs), showcasing robust anti-calcification and anti-thrombosis properties post fatigue testing. Post-implantation, the DHVs could adaptively degrade during recellularization, releasing H2S to further support tissue regeneration. Therefore, the comprehensive endothelial cell coverage and notable extracellular matrix remodeling could be clearly observed. This accessible and integrated strategy effectively overcomes various limitations of bioprosthetic valves, showing promise as an attractive approach for immune modulation of biomaterials.

Surface functionalization of polyurethanes: A critical review

Synthetic polymers, particularly polyurethanes (PUs), have revolutionized bioengineering and biomedical devices due to their customizable mechanical properties and long-term stability. However, the inherent hydrophobic nature of PU surfaces arises common issues such as high friction, strong protein adsorption, and thrombosis, especially in the physiological environment of blood contact. To overcome these issues, researchers have explored various modification techniques to improve the surface biofunctionality of PUs. In this review, we have systematically summarized several typical surface modification methods including surface plasma modification, surface oxidation-induced grafting polymerization, isocyanate-based chemistry coupling, UV-induced surface grafting polymerization, adhesives-assisted attachment strategy, small molecules-bridge grafting, solvent evaporation technique, and hydrogen bonding interaction. Correspondingly, the advantages, limitations, and future prospects of these surface modification methods were discussed. This review provides an important guidance or tool for developing surface functionalized PUs in the fields of bioengineering and medical devices.

Functionalization of in vivo tissue-engineered living biotubes enhance patency and endothelization without the requirement of systemic anticoagulant administration

Vascular regeneration and patency maintenance, without anticoagulant administration, represent key developmental trends to enhance small-diameter vascular grafts (SDVG) performance. In vivo engineered autologous biotubes have emerged as SDVG candidates with pro-regenerative properties. However, mechanical failure coupled with thrombus formation hinder translational prospects of biotubes as SDVGs. Previously fabricated poly(ε-caprolactone) skeleton-reinforced biotubes (PBs) circumvented mechanical issues and achieved vascular regeneration, but orally administered anticoagulants were required. Here, highly efficient and biocompatible functional modifications were introduced to living cells on PB lumens. The 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-methoxy (DMPE)-PEG-conjugated anti-coagulant bivalirudin (DPB) and DMPE-PEG-conjugated endothelial progenitor cell (EPC)-binding TPS-peptide (DPT) modifications possessed functionality conducive to promoting vascular graft patency. Co-modification of DPB and DPT swiftly attained luminal saturation without influencing cell viability. DPB repellent of non-specific proteins, DPB inhibition of thrombus formation, and DPB protection against functional masking of DPT's EPC-capture by blood components, which promoted patency and rapid endothelialization in rat and canine artery implantation models without anticoagulant administration. This strategy offers a safe, facile, and fast technical approach to convey additional functionalization to living cells within tissue-engineered constructs.

Chitosan Hydrogel as Tissue Engineering Scaffolds for Vascular Regeneration Applications

Chitosan hydrogels have a wide range of applications in tissue engineering scaffolds, mainly due to the advantages of their chemical and physical properties. This review focuses on the application of chitosan hydrogels in tissue engineering scaffolds for vascular regeneration. We have mainly introduced these following aspects: advantages and progress of chitosan hydrogels in vascular regeneration hydrogels and the modification of chitosan hydrogels to improve the application in vascular regeneration. Finally, this paper discusses the prospects of chitosan hydrogels for vascular regeneration.

Improved Hemocompatibility on Superhemophobic Micro-Nano-Structured Titanium Surfaces

Blood-contacting titanium-based implants such as endovascular stents and heart valve casings are prone to blood clotting due to improper interactions at the surface level. In complement, the current clinical demand for cardiovascular implants is at a new apex. Hence, there is a crucial necessity to fabricate an implant with optimal mechanical properties and improved blood compatibility, while simultaneously interacting differentially with cells and other microbial agents. The present study intends to develop a superhydrophobic implant surface with the novel micro-nano topography, developed using a facile thermochemical process. The surface topography, apparent contact angle, and crystal structure are characterized on different surfaces. The hemo/blood compatibility on different surfaces is assessed by evaluating hemolysis, fibrinogen adsorption, cell adhesion and identification, thrombin generation, complement activation, and whole blood clotting kinetics. The results indicate that the super-hemo/hydrophobic micro-nano titanium surface improved hemocompatibility by significantly reducing fibrinogen adsorption, platelet adhesion, and leukocyte adhesion. Thus, the developed surface has high potential to be used as an implant. Further studies are directed towards analyzing the mechanisms causing the improved hemocompatibility of micro/nano surface features under dynamic in vitro and in vivo conditions.

Advances in Electrostatic Spinning of Polymer Fibers Functionalized with Metal-Based Nanocrystals and Biomedical Applications

Considering the metal-based nanocrystal (NC) hierarchical structure requirements in many real applications, starting from basic synthesis principles of electrostatic spinning technology, the formation of functionalized fibrous materials with inorganic metallic and semiconductor nanocrystalline materials by electrostatic spinning synthesis technology in recent years was reviewed. Several typical electrostatic spinning synthesis methods for nanocrystalline materials in polymers are presented. Finally, the specific applications and perspectives of such electrostatic spun nanofibers in the biomedical field are reviewed in terms of antimicrobial fibers, biosensing and so on.

Decellularized Scaffold-based Poly(ethylene glycol) Biomimetic Vascular Patches Modified with Polyelectrolyte Multilayer of Heparin and Chitosan: Preparation and Vascular Tissue Engineering Applications in a Porcine Model

The mechanical property mismatch between vascular patches and native blood vessels can result in post-operation failure, so it is important to develop vascular patches that mimic the biomechanical properties of...

End-Point Immobilization of Heparin on Electrospun Polycarbonate-Urethane Vascular Graft

There is a tremendous clinical need for synthetic vascular grafts either for bypass procedure or vascular access during hemodialysis. However, currently, there is no small-diameter vascular graft commercially available to meet long-term patency requirement due to frequent thrombus formation and intimal hyperplasia. This chapter describes the fabrication of electrospun small-diameter polycarbonate-urethane (PCU) vascular graft with a biomimetic fibrous structure. Additionally, the surface of the vascular graft is aminated via plasma treatment for the subsequently end-point heparin immobilization to enhance antithrombosis property.

Heparin detection based on the fluorescent turn-on probe of amino carbon quantum dots

Amino-rich carbon quantum dots (CDs) were synthesized by hydrothermal treatment of ethylene glycol, glucose and polyethyleneimine. CDs have green fluorescence (excitation/emission peaks 435 nm/515 nm) and can be enhanced by the addition of heparin (Hep). A linear relationship between fluorescence intensity and heparin concentration was observed. The fluorescence turn-on probe used for Hep detection showed a very large detection range of 0.02-16 μM, covering different therapeutic ranges in clinical applications. The probe exhibited an ultra-low detection limit of 0.007 nM.

Glycosaminoglycans: From Vascular Physiology to Tissue Engineering Applications

Cardiovascular diseases represent the number one cause of death globally, with atherosclerosis a major contributor. Despite the clinical need for functional arterial substitutes, success has been limited to arterial replacements of large-caliber vessels (diameter > 6 mm), leaving the bulk of demand unmet. In this respect, one of the most challenging goals in tissue engineering is to design a "bioactive" resorbable scaffold, analogous to the natural extracellular matrix (ECM), able to guide the process of vascular tissue regeneration. Besides adequate mechanical properties to sustain the hemodynamic flow forces, scaffold's properties should include biocompatibility, controlled biodegradability with non-toxic products, low inflammatory/thrombotic potential, porosity, and a specific combination of molecular signals allowing vascular cells to attach, proliferate and synthesize their own ECM. Different fabrication methods, such as phase separation, self-assembly and electrospinning are currently used to obtain nanofibrous scaffolds with a well-organized architecture and mechanical properties suitable for vascular tissue regeneration. However, several studies have shown that naked scaffolds, although fabricated with biocompatible polymers, represent a poor substrate to be populated by vascular cells. In this respect, surface functionalization with bioactive natural molecules, such as collagen, elastin, fibrinogen, silk fibroin, alginate, chitosan, dextran, glycosaminoglycans (GAGs), and growth factors has proven to be effective. GAGs are complex anionic unbranched heteropolysaccharides that represent major structural and functional ECM components of connective tissues. GAGs are very heterogeneous in terms of type of repeating disaccharide unit, relative molecular mass, charge density, degree and pattern of sulfation, degree of epimerization and physicochemical properties. These molecules participate in a number of vascular events such as the regulation of vascular permeability, lipid metabolism, hemostasis, and thrombosis, but also interact with vascular cells, growth factors, and cytokines to modulate cell adhesion, migration, and proliferation. The primary goal of this review is to perform a critical analysis of the last twenty-years of literature in which GAGs have been used as molecular cues, able to guide the processes leading to correct endothelialization and neo-artery formation, as well as to provide readers with an overall picture of their potential as functional molecules for small-diameter vascular regeneration.

Synthesis, Characterization, and Electrospinning of a Functionalizable, Polycaprolactone-Based Polyurethane for Soft Tissue Engineering

We synthesized a biodegradable, elastomeric, and functionalizable polyurethane (PU) that can be electrospun for use as a scaffold in soft tissue engineering. The PU was synthesized from polycaprolactone diol, hexamethylene diisocyanate, and dimethylolpropionic acid (DMPA) chain extender using two-step polymerization and designated as PU-DMPA. A control PU using 1,4-butanediol (1,4-BDO) as a chain extender was synthesized similarly and designated as PU-BDO. The chemical structure of the two PUs was verified by FT-IR and ¹H-NMR. The PU-DMPA had a lower molecular weight than the PU-BDO (~16,700 Da vs. ~78,600 Da). The melting enthalpy of the PU-DMPA was greater than that of the PU-BDO. Both the PUs exhibited elastomeric behaviors with a comparable elongation at break (λ=L/L0= 13.2). The PU-DMPA had a higher initial modulus (19.8 MPa vs. 8.7 MPa) and a lower linear modulus (0.7 MPa vs. 1.2 MPa) and ultimate strength (9.5 MPa vs. 13.8 MPa) than the PU-BDO. The PU-DMPA had better hydrophilicity than the PU-BDO. Both the PUs displayed no cytotoxicity, although the adhesion of human umbilical artery smooth muscle cells on the PU-DMPA surface was better. Bead free electrospun PU-DMPA membranes with a narrow fiber diameter distribution were successfully fabricated. As a demonstration of its functionalizability, gelatin was conjugated to the electrospun PU-DMPA membrane using carbodiimide chemistry. Moreover, hyaluronic acid was immobilized on the amino-functionalized PU-DMPA. In conclusion, the PU-DMPA has the potential to be used as a scaffold material for soft tissue engineering.

Peptide grafting strategies before and after electrospinning of nanofibers

Nanofiber films produced by electrospinning currently provide a promising platform for different applications. Although nonfunctionalized nanofiber films from natural or synthetic polymers are extensively used, electrospun materials combined with peptides are gaining more interest. In fact, the selection of specific peptides improves the performance of the material for biological applications and mainly for tissue engineering, mostly by maintaining similar mechanical properties with respect to the simple polymer. The main drawback in using peptides blended with a polymer is the quick release of the peptides. To avoid this problem, covalent linking of the peptide is more beneficial. Here, we reviewed synthetic protocols that enable covalent grafting of peptides to polymers before or after the electrospinning procedures to obtain more robust electrospun materials. Applications and the performance of the new material compared to that of the starting polymer are discussed.

Electrospinning for healthcare: recent advancements

This perspective explores recent developments and innovations in the electrospinning technique and their potential applications in biomedicine.

Covalent grafting of PEG and heparin improves biological performance of electrospun vascular grafts for carotid artery replacement

Rapid endothelialization of small-diameter vascular grafts remains a significant challenge in clinical practice. In addition, compliance mismatch causes intimal hyperplasia and finally leads to graft failure. To achieve compliance match and rapid endothelialization, we synthesized low-initial-modulus poly(ester-urethane)urea (PEUU) elastomer and prepared it into electrospun tubular grafts and then functionalized the grafts with poly(ethylene glycol) (PEG) and heparin via covalent grafting. The PEG- and heparin-functionalized PEUU (PEUU@PEG-Hep) graft had comparable mechanical properties with the native blood vessel. In vitro data demonstrated that the grafts are of good cytocompatibility and blood compatibility. Covalent grafting of PEG and heparin significantly promoted the adhesion, spreading, and proliferation of human umbilical vein endothelial cells (HUVECs) and upregulated the expression of vascular endothelial cell-related genes, as well as increased the capability of grafts in preventing platelet deposition. In vivo assessments indicated good biocompatibility of the PEUU@PEG-Hep graft as it did not induce severe immune responses. Replacement of resected carotid artery with the PEUU@PEG-Hep graft in a rabbit model showed that the graft was capable of rapid endothelialization, initiated vascular remodeling, and maintained patency. This study demonstrates the PEUU@PEG-Hep vascular graft with compliance match and efficacious antithrombosis might find opportunities for bioactive blood vessel substitutes.

Preparation of phospholipid-based polycarbonate urethanes for potential applications of blood-contacting implants

Polyurethanes are widely used in interventional devices due to the excellent physicochemical property. However, non-specific adhesion and severe inflammatory response of ordinary polyurethanes may lead to severe complications of intravenous devices. Herein, a novel phospholipid-based polycarbonate urethanes (PCUs) were developed via two-step solution polymerization by direct synthesis based on functional raw materials. Furthermore, PCUs were coated on biomedical metal sheets to construct biomimetic anti-fouling surface. The results of stress–strain curves exhibited excellent tensile properties of PCUs films. Differential scanning calorimetry results indicated that the microphase separation of such PCUs polymers could be well regulated by adjusting the formulation of chain extender, leading to different biological response. In vitro blood compatibility tests including bovine serum albumin adsorption, fibrinogen adsorption and denaturation, platelet adhesion and whole-blood experiment showed superior performance in inhibition non-specific adhesion of PCUs samples. Endothelial cells and smooth muscle cells culture tests further revealed a good anti-cell adhesion ability. Finally, animal experiments including ex vivo blood circulation and subcutaneous inflammation animal experiments indicated a strong ability in anti-thrombosis and histocompatibility. These results high light the strong anti-adhesion property of phospholipid-based PCUs films, which may be applied to the blood-contacting implants such as intravenous catheter or antithrombotic surface in the future.

Surface Engineering of Cardiovascular Devices for Improved Hemocompatibility and Rapid Endothelialization

Cardiovascular devices have been widely applied in the clinical treatment of cardiovascular diseases. However, poor hemocompatibility and slow endothelialization on their surface still exist. Numerous surface engineering strategies have mainly sought to modify the device surface through physical, chemical, and biological approaches to improve surface hemocompatibility and endothelialization. The alteration of physical characteristics and pattern topographies brings some hopeful outcomes and plays a notable role in this respect. The chemical and biological approaches can provide potential signs of success in the endothelialization of vascular device surfaces. They usually involve therapeutic drugs, specific peptides, adhesive proteins, antibodies, growth factors and nitric oxide (NO) donors. The gene engineering can enhance the proliferation, growth, and migration of vascular cells, thus boosting the endothelialization. In this review, the surface engineering strategies are highlighted and summarized to improve hemocompatibility and rapid endothelialization on the cardiovascular devices. The potential outlook is also briefly discussed to help guide endothelialization strategies and inspire further innovations. It is hoped that this review can assist with the surface engineering of cardiovascular devices and promote future advancements in this emerging research field.

Recent advances in tissue engineering scaffolds based on polyurethane and modified polyurethane

Organ repair, regeneration, and transplantation are constantly in demand due to various acute, chronic, congenital, and infectious diseases. Apart from traditional remedies, tissue engineering (TE) is among the most effective methods for the repair of damaged tissues via merging the cells, growth factors, and scaffolds. With regards to TE scaffold fabrication technology, polyurethane (PU), a high-performance medical grade synthetic polymer and bioactive material has gained significant attention. PU possesses exclusive biocompatibility, biodegradability, and modifiable chemical, mechanical and thermal properties, owing to its unique structure-properties relationship. During the past few decades, PU TE scaffold bioactive properties have been incorporated or enhanced with biodegradable, electroactive, surface-functionalised, ayurvedic products, ceramics, glass, growth factors, metals, and natural polymers, resulting in the formation of modified polyurethanes (MPUs). This review focuses on the recent advances of PU/MPU scaffolds, especially on the biomedical applications in soft and hard tissue engineering and regenerative medicine. The scientific issues with regards to the PU/MPU scaffolds, such as biodegradation, electroactivity, surface functionalisation, and incorporation of active moieties are also highlighted along with some suggestions for future work.

Terminal Group Modification of Carbon Nanotubes Determines Covalently Bound Osteogenic Peptide Performance

Osteogenic peptides are often introduced to improve biological activities and the osteogenic ability of artificial bone materials as an effective approach. Covalent bindings between the peptide and the host material can increase the molecular interactions and make the functionalized surface more stable. However, covalent bindings through different functional groups can bring different effects on the overall bioactivities. In this study, carboxyl and amino groups were respectively introduced onto carbon nanotubes, a nanoreinforcement for synthetic scaffold materials, which were subsequently covalently attached to the RGD/BMP-2 osteogenic peptide. MC3T3-E1 cells were cultured on scaffolds containing peptide-modified carbon nanotubes. The results showed that the peptide through the amino group binding could promote cell functions more effectively than those through carboxyl groups. The mechanism may be that the amino group could bring more positive charges to carbon nanotube surfaces, which further led to differences in the peptide conformation, protein adsorption, and targeting osteogenic effects. Our results provided an effective way of improving the bioactivities of artificial bone materials by chemically binding osteogenic peptides.

State of the Art of Small-Diameter Vessel-Polyurethane Substitutes

Cardiovascular diseases are a severe threat to human health. Implantation of small-diameter vascular substitutes is a promising therapy in clinical operations. Polyurethane (PU) is considered one of the most suitable materials for this substitution due to its good mechanical properties, controlled biostability, and proper biocompatibility. According to biodegradability and biostability, in this review, PU small-diameter vascular substitutes are divided into two groups: biodegradable scaffolds and biostable prostheses, which are applied to the body for short- and long-term, respectively. Following this category, the degradation principles and mechanisms of different kinds of PUs are first discussed; then the chemical and physical methods for adjusting the properties and the research advances are summarized. On the basis of these discussions, the problems remaining at present are addressed, and the contour of future research and development of PU-based small-diameter vascular substitutes toward clinical applications is outlined.

Enhancing anti-thrombogenicity of biodegradable polyurethanes through drug molecule incorporation

Sufficient and sustained anti-thrombogenicity is essential for blood-contacting materials, because blood coagulation and thrombosis caused by platelet adhesion and activation on material surfaces may lead to functional failure and even fatal outcomes. Covalently conjugating antithrombogenic moieties into polymer, instead of surface modifying or blending, can maintain the anti-thrombogenicity of polymer at a high level over a time range. In this study, series of randomly crosslinked, elastic, biodegradable polyurethanes (PU-DPA) were synthesized through a one-pot and one-step method from polycaprolactone (PCL) diol, hexamethylene diisocyanate (HDI) and anti-thrombogenic drug, dipyridamole (DPA). The mechanical properties, hydrophilicity, in vitro degradation, and anti-thrombogenicity of the resultant PU-DPA polymers can be tuned by altering the incorporated DPA amount. The surface and bulk hydrophilicity of the polyurethanes decreased with increasing hydrophobic DPA amount. All PU-DPA polymers exhibited strong mechanical properties and good elasticity. The degradation rates of the PU-DPAs decreased with increasing DPA content in both PBS and lipase/PBS solutions. Covalently incorporating DPA into the polyurethane significantly reduced the platelet adhesion and activation compared to the polyurethane without DPA, and also can achieve sustained anti-thrombogenicity. The PU-DPA films also supported the growth of human umbilical vein endothelial cells. The attractive mechanical properties, blood compatibility, and cell compatibility of this anti-thrombogenic biodegradable polyurethane indicate that it has a great potential to be utilized for blood-contacting devices, and cardiovascular tissue repair and regeneration.

Accurate and continuous ultrasonography evaluation of small diameter vascular prostheses in vivo

There is a large clinical requirement for novel vascular grafts; however, the development of novel vascular grafts has not been extremely successful to date. The most successful method for the continuous evaluation of vascular grafts in vivo remains unclear. Therefore, an optimal successive, non-invasive imaging modality is necessary for the study of vascular transplantation. In the present study, a common rabbit model of carotid artery defect was utilized. The patency and hemodynamic characteristics of implanted grafts was examined following surgery by color Doppler ultrasound in three modes, including B-mode, color flow map and pulse-Doppler examination. The results revealed that ultrasound had sufficient spatial resolution to generate clear images of the carotid artery of rabbits with or without the implanted grafts. Color Doppler ultrasound may be applied to evaluate and differentiate the patent, stenosis and occlusion of carotid arteries in rabbits with different vascular grafts implanted. Furthermore, color Doppler ultrasound is an optimal imaging modality for continuous evaluation in vivo. It is also possible for some quantitative analyses to be performed, including measuring the diameter of vascular lumens and the flow velocity of the region of interest. The present study suggests vascular ultrasound as the optimum choice for continuous surveillance of vascular prostheses in vivo, which may provide valuable information about the grafts in order to greatly shorten the experimental period.

A multifunctional surface for blood contact with fibrinolytic activity, ability to promote endothelial cell adhesion and inhibit smooth muscle cell adhesion

A multifunctional surface with fibrinolytic activity, the ability to promote endothelial cell and inhibit smooth muscle cell adhesion was realized.